File Photo: A giant mosquito with a wing span of 11.15 centimeters is shown at the Insect Museum of West China in Chengdu, capital of SW China's Sichuan Province, April 11, 2018. (Xinhua/Insect Museum of West China)

NEW YORK, June 20 (Xinhua) -- New York City has begun its first aerial larvicide treatment to large natural areas to control the risk of mosquito-borne disease.

Low-flying helicopters will be spraying marshes and other nonresidential areas of the boroughs of Staten Island, Brooklyn, Queens and the Bronx from Tuesday to Thursday between the hours of 6 a.m. and 7 p.m., according to the city's Health Department.

In case of bad weather, the application will be delayed until Wednesday to Friday during the same hours.

The department also applies pesticides to mosquito breeding grounds when appropriate throughout the summer.

Last year, there were 21 cases of West Nile virus in the city, and two deaths were attributed to the disease.